The Chesapeake Bay Program projects that despite heavier rains and low winds, the Bay dead zone is expected to remain slightly above average.
Researchers from the Chesapeake Bay Program, University of Maryland Center for Environmental Science, University of Michigan and U.S. Geological Survey announced last week that they are predicting this year’s Chesapeake Bay dead zone to be just above the long-term average taken between 1985 and 2023, despite above-average rainfall in spring 2024 that led to relatively high water flows entering the Bay from around the watershed. Experts also noted that the dead zone likely began earlier this year due to warmer-than-normal temperatures throughout the spring as well as weaker winds.
Nitrogen and phosphorus (referred to together as “nutrients”) pollution that runs off from across the Bay watershed spurs the growth of algae blooms, which remove oxygen from the water when they die off. These low-oxygen sections of the Bay, known as hypoxic areas or “dead zones,” can suffocate marine life and shrink the habitat available to fish, crabs and other critters.
Due to higher-than-average precipitation, stream and river flows to the Chesapeake Bay recorded from January—May 2024 were 63% higher than the previous year and 23% higher than the long-term average. Based on this information, researchers estimate that the total annual hypoxic volume for the Bay in 2024 will be just 4% higher than the historic long-term average.
Additionally, from January—May 2024, 131 million pounds of nitrogen entered the Bay as measured at the River Input Monitoring (RIM) stations located on the Chesapeake’s nine largest tributaries, representing about 78% of the total area of the watershed. The amount of nitrogen entering the Bay in 2024 was approximately 77% higher than last year, when below-average rainfall brought about 74 million pounds of nitrogen into the Chesapeake. However, the amount of nitrogen pollution entering the Bay in 2024 is roughly equal to the long-term average (1985-2023).
In the areas of the Bay not monitored by the RIM stations, additional pollution is reported from wastewater treatment plants and included in the forecast. In 2024, 4.7 million pounds of nitrogen were recorded flowing into the Chesapeake between January and May, which is less than the 5.2 million pounds recorded in 2023 and the 5.7 million pounds recorded in 2022.
The slightly above-average estimated hypoxic volume following a season of relatively high stream and river flows indicate that management efforts to keep nutrient runoff out of the Bay watershed is having the desired effect.
In the fall of 2024, researchers will follow up on this forecast with a Bay-wide assessment of the dead zone size and duration.
